For various reasons, it may be necessary in exhaust systems of internal combustion engines to introduce a liquid educt into the exhaust gas flow. For example, fuel may be injected into the exhaust gas flow upstream of an oxidation-type catalytic converter in order to trigger an exothermal combustion reaction at the oxidation-type catalytic converter arranged downstream. For example, a reducing agent, for example, ammonia, may likewise be injected into the exhaust gas flow in order to reduce nitrogen oxides carried in the exhaust gas flow in an SCR catalytic converter arranged downstream. Urea or an aqueous urea solution may also be injected into the exhaust gas flow instead of ammonia. Ammonia and water will then be formed from the urea-water solution by a hydrolysis reaction. Furthermore, a fuel or another suitable reducing agent may be injected into the exhaust gas flow upstream of an NOx storage catalyst in order to regenerate the NOx storage catalyst.
To improve or make possible the mode of action of the educt injected in the liquid form into the exhaust gas line, extensive evaporation is just as desirable as intense mixing with the exhaust gas in order to thus obtain the most homogeneous exhaust gas-educt mixture possible. The exhaust system may be equipped for this with a mixing and/or evaporating device arranged downstream in the exhaust gas line.
Such a mixing and/or evaporating device, which has a plurality of blades, which are arranged distributed in the circumferential direction and project each towards the inside from an outer wall, is known from DE 10 2007 028 449 A1. Each blade has a profile at least in an area adjoining the outer wall in the axial direction, at which a discharge edge has an offset in the circumferential direction in relation to a leading edge. The blades correspondingly have an angle of incidence in relation to the exhaust gas flow, as a result of which they can impose a twist on the exhaust gas flow. Furthermore, it is possible due to the blades having an angle of incidence to shape and arrange the blades such that they mutually overlap in the circumferential direction, as a result of which an annular surface, which is opaque in the axial direction, can be generated, which effectively hinders or even prevents the breakthrough of droplets through the mixing and/or evaporating device.
However, the swirling or twist generation, which can be brought about by means of such a prior-art mixing and/or evaporating device in the exhaust gas flow, is accompanied by an increase in pressure, which has a negative effect on the performance and efficiency of an internal combustion engine equipped with the exhaust system.